1. Field of the Invention
The invention generally relates to an atomic layer deposition (ALD) system. More particularly, the invention relates to an improved plasma enhanced atomic layer deposition (PEALD) system.
2. Description of the Prior Art
The technology of ALD (atomic layer deposition) has been developed to form thin dielectric films on substrates. In the method of ALD, gas chemically reacts with the surface of a substrate and attaches to it to form a layer with the atom-scale thickness thanks to the self-limiting characteristic of such reaction. In comparison to the traditional film forming technology, the technology of ALD has the advantages of higher coverage rate and more evenness in the thickness of the films.
To lower the necessary temperature in the film forming process, the technology of PEALD (plasma enhanced atomic layer deposition) has been developed. In comparison to the technology of ALD, the technology of PEALD has the advantages of lower temperature in the process, smoother surface of the thin films, better conductive properties and shorter time in production. In the PEALD system of the prior art, the PEALD system comprises a single quartz tubular unit, a processing chamber and a gate valve. The single quartz tubular unit is in communication with the processing chamber. The gate valve is provided on the single quartz tubular unit so as to control the entry of plasma and thus the formation of the ALD on the substrates.
In addition, in the forming process, the gate valve has to be opened and closed frequently to avoid the precursor from forming a chemical vapor deposition (CVD) on a substrate. Therefore, before the gate valve is closed, a small amount of the precursor may already enter the quartz tubular unit and then react with the plasma to form a CVD. In such case, the thin films of the finished substrates may be adversely affected. Moreover, the gate valve does not have a diffusion design so that plasma flowing from the gate valve can not evenly distribute on the entirety of a substrate. This adversely affects the quality of the finished substrates. In addition, because the gate valve is opened and closed frequently, the maintenance cost of the gate valve is quite high.
To eliminate these disadvantages, the inventor of the present invention has put a lot of effort into the subject and has successfully come up with the improved PEALD system of the present invention.